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Unformatted text preview: 1 The Cytoskeleton of Eukaryotic Cells A Network of Skeletal Fibers that is Continually Changing its Shape Functions: Cell Structure and Movement The Cytoskeleton The three main kinds of bers are: Actin flaments-also called Microflaments, (7 nm diameter) made oF the protein, actin Microtubules (25 nm diameter) made oF the protein, tubulin Intermediate flaments made oF many diFFerent proteins 2 Actin Filaments 3 Figure 4.19 Showing Cause and Effect in Biology Actin Filaments (Microflaments) The flaments look like 2 inter-twined strings o beads Occurs in bundles containing many actin flaments and in complex networks 4 Some Important Properties of Actin Filaments They polymerize (self assemble) by noncovalent, reversible, addition of actin monomers at the ends of the laments- are highly dynamic A fundamental capability of biological molecules is the ability to self-assemble Some Important Properties of Actin Filaments They polymerize (self assemble) by noncovalent, reversible, addition of actin monomers at the ends (tips) of the laments (A fundamental capability of many biological molecules is the ability to self-assemble) ATP is hydrolyzed during assembly, causing a special type of dynamic activity called treadmilling (assembly at one end of the lament and disassembly at the opposite end----the laments are polar) There are many actin-associated proteins that tell the actin laments how to assemble and what to do 5 Two Main Functions of Actin Filaments Determining cell shape and changing cell shape Cell movement (cell motility) Movement of cells from one place to another, movements inside cells For example, making a cell long and thin or changing the shape to short and thick 6 Three Examples of Actin Filaments in Structural Support Stress Fibers (bundles of actin laments) help keep cells elongated and stiff 7 Three Examples of Actin Filaments in Structural Support stress bers (bundles of actin laments) Fig 4.20 part A Microvilli (relatively stable actin bundles projecting from the cell surface) increases the cells surface area Figure 4.21 Microfilaments for Support 8 Cartoon Diagram of a Brush Border Microvillus Actin Flaments Actin-linking proteins Epithelial Cell Brush Borders ig. 4.22 Increases surface area of cells- for absorption of nutrients 9 Three Examples of Actin Filaments in Structural Support stress bers (bundles of actin laments) microvilli (relatively stable actin bundles at the cell surface that increase the cells surface area) focal adhesions- places of attachment of the cytoskeleton to the cell membrane The Actin Cytoskeleton Anchors the Plasma Membrane to the Cytoplasm at Focal Adhesions Membrane anchorage through actin-associated proteins (ankyrin, spectrin) and actin 10 Actin Filaments Microtubules See part C Microtubules Hollow tubes (25 nm) Made of the protein, tubulin, a dimer Main Functions:-Maintenance of cell shape-Changing cell shape- Cell movement 11...
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